JohnW, Xavier has given you your answer which basically is "where you are using the computer".However the male plug on the end of the computer power cord will only fit into a 110v or a 220v (not both) the 220v plugs vary depending on the wattage capability but they are ALL different that the 110v male plug and won't go into a 110v outlet. If you are running the computer in a 220v country and you have a 110v plug you will need to change it and then select 220v on the rear choice switch.truenorth
